It's about validation and evaluating our lives through others, real or fictional, instead of our own accomplishments. Severe cases result in confusing fiction and reality. It's the same effect as when an audience perceives an actor of a character we admire as having disliked the role and being unappreciative of the audience. See reaction to Nimoy's "I Am Not Spock" book or Shatner's "Get A Life" skit on Saturday Night Live years ago. Their intent was much different than fan interpretation.